If I could tell you one thing before the start of a semester... well, I can't. There are too many things to tell you all at once. But here are some basic things to remember:
1) The military taught you how to be in the military. They didn't teach you how to do well in college.
2) Most of your fellow students won't care that you were in central Afghanistan any more than you will care that they were raised on a farm in central Iowa. It's not that they don't support you or appreciate what you did for your country-- they do-- but right now college is life for them, as it should be for you.
3) No one will follow you around asking if you're doing all right in your classes. It is very easy to fall behind-- all it takes is missing one assignment. If you are having trouble completing an assignment or getting a concept down, ask for help. Talk to your professor and/or your teaching assistant(s).
4) Orientation probably won't tell you everything you need to know. Find people with school name tags and ask them questions.
5) Find some other vets. See if there's a student veterans group you can join. If you see someone walking down the street humping a pack with unit patches still attached, say hi.
Finally, and most important-- this college shit is hard. Accept that at times, you will struggle. Understand that everyone else around you is busting ass too. That's why degrees are earned, not simply given out.
Have a good semester :)
(If you have questions about anything school related, you're invited to ask-- I can only answer based on my experience, but hopefully that will help.)